Abstract

A joint experimental and numerical study on the characterisation of shear flow mixing and turbulence in the flow behind a CRUF (counter rotating ultrahigh-bypass fan)-TPS (turbine power simulator) has been performed at the Institute of Aerodynamics and Flow Technology of DLR in order to engross the understanding of such flows, enable a direct comparison of both methods and provide data for the validation of numerical codes.
Stereo PIV measurements with very high spatial resolution have been carried out at the low speed wind tunnel of DNW-NWB by using two 11 megapixels PCO4000 cameras and a high power Nd-YAG double pulse laser with 380 mJ per pulse output energy. A forward scattering SPIV set-up was used in a plane perpendicular to the main flow and x = 450 mm downstream of the CRUF-TPS core trailing-edge in order to measure all three components of a large number of instantaneous velocity vector fields in a region of 330 x 410 mm² for many different flow and TPS conditions. A second SPIV set-up was realized in order to measure the velocity fields in a plane parallel to the main flow depicturing the shear layer developments between free stream, fan flow, and core flow between x = 20 and x = 370 mm downstream of the CRUF trailing-edge for the same flow parameter matrix. For all cases both, a phase-locked triggering to a fixed fan blade position and a random triggering of the PIV system have been applied. This enables analysing the differences between periodic and non-periodic effects of the turbulence mixing in the shear layers. For evaluation of the PIV images an iterative multi-grid cross-correlation scheme with image deformation has been applied with 32 x 32 pixels² final window resolution leading to instantaneous velocity vector fields with more than 70000 3C-vectors each. A number of 1000 double images have been acquired per case for reaching convergence of the averages and rms-values.
In advance to the SPIV campaign five-hole-probe rake measurements have been performed in several planes downstream of the CRUF-TPS.